1. Field of the Invention
The present invention relates to a spindle motor and a disk drive apparatus.
2. Description of the Related Art
In accordance with increased storage density of disks, there has been a demand for disk drive apparatuses, such as, for example, hard disk drives, to control rotation of the disks, movement of heads, and so on with high precision. In a known hard disk drive (HDD) disclosed in JP-A 2006-40423, a gas arranged in an interior of the HDD is a low-density gas, such as, for example, a helium gas or a hydrogen gas, and the HDD is thus arranged to achieve a reduction in resistance of the gas against a disk, a head, and so on during rotation of a spindle motor. The reduction in the resistance of the gas against the disk, the head, and so on contributes to reducing vibration of the disk, the head, and so on, enabling highly precise data recording. Such a disk drive apparatus includes a base defined by machining a plate material, such as, for example, an SPCC plate, or a casting of an aluminum-based alloy.
Bases of some spindle motors (hereinafter referred to simply as “motors”) installed in HDDs are defined by portions of housings of the HDDs. In the case where the interior of the HDD is filled with a gas such as a helium gas or the like as described in JP-A 2006-40423, the helium gas, for example, which has extremely small molecules, tends to easily leak out of the interior of the HDD to an outside of the HDD. In the case of such a spindle motor, a base of the spindle motor is produced by casting, and accordingly, a blowhole may be defined in the base. Such a blowhole is, for example, exposed on a surface of the base, which has been subjected to a cutting process. Thus, the blowhole may join a space inside the base to a space outside the base through the surface of the base which has been subjected to the cutting process. If this happens, a gas, such as a helium gas or the like, which is arranged in the space inside the base may leak out to the space outside the base.